Prior art of possible relevance includes U.S. Pat. No. 2,317,519 issued Apr. 27, 1943 to Coons and U.S. Pat. No. 3,495,657 issued Feb. 17, 1970 to Keith. Also of possible relevance is an article entitled "Heat Transfer and Pressure Drop Characteristics of Fin Tubes in Cross Flow" by Kenichi Hashizume published in Heat Transfer Engineering Vol. 3, No. 2, October-December, 1981, pages 15-20, inclusive and Japanese patent application laid open No. 57-105689.
Many heat exchangers employ cores constructed of one or more tubes through which a heat exchange fluid may flow and which are provided with external, generally radially extending, fins. Such cores may be divided into two general groups, namely, smooth finned and segmented fin.
In the case of smooth finned cores, plate-like elements are secured by any of a variety of means to the tubes. In the segmented fin type, a radially outwardly extending fin is cut at closely spaced intervals to provide radially outwardly extending spines.
Generally speaking, the segmented fin constructions have better heat exchange performance than otherwise identical smooth finned constructions. This is due to the fact that the spines constituting the segmented fin increase the turbulence of the fluid passing therethrough thereby decreasing the thickness of the boundary layer and providing an increased rate of heat transfer.
At the same time, because of the increased turbulence, a greater pressure drop will be experienced across a segmented fin core than across an otherwise identical smooth finned core due to increase resistance to fluid flow caused by the presence of the spines constituting the segmented fin.
Where the fluid is propelled by a fan or the like, the higher pressure drop requires the use of a larger motor for driving the fan with the accompanying increase in energy requirements. In the usual case, the tubes carry a heat transfer medium subject to heating or cooling by the flow of a fluid, most typically air, across the fins and the tubes. The pressure drop, and thus the energy requirement to pass a fluid through the fins is related to what might be termed "spine density", that is, the number of spines in a given volume through which the fluid must pass.
At the same time, the overall heat transfer coefficient of such structures is largely controlled by the air or fluid side heat transfer coefficient and the effectively air side area over which heat transfer may occur.
When air or fluid flows across a row or rows of tubes having conventional fins, recirculation zones are formed in the downstream side of the tubes. These recirculation zones are areas of relatively low localized air velocity with the consequence that the air side heat transfer coefficient in such areas are relatively low and the finned heat transfer area in such zone is not utilized effectively.
Similarly, it has been found that localized areas of low air velocity may exist near the roots of conventional fins on the upstream side of the tube. And, of course, where fins are segmented, there is an increase to the resistance to air flow as mentioned previously. This may increase the size of the recirculation zone downstream of the tube as well as decrease the local air velocity both upstream and downstream of the tube which reduce the effectiveness of the fin in such areas. Consequently, there is underutilization of the fin material in one or the other of such areas. Such underutilized material not only adds to the cost of manufacture of the core, but increases the size of the same as well as the air side pressure drop.
The present invention is directed to overcoming one or more of the above problems.